The objective is to develop a pump energized by skeletal muscle (skeletal muscle ventricle or SMV) to be used for left heart assist in the estimated 10,000 patients who present annually in the United States with irreversible heart failure. During the past 12 years of NIH funding, this research has progressed from a concept that might be possible, to an SMV that pumped blood in the circulation for several hours indicating that muscle fatigue was no longer a major obstacle, to an SMV that has pumped blood effectively in the circulation beyond four years. During this current funding period, existing successful SMV models were modified to make them clinically applicable. Further refinement and testing, including during chronic heart failure, are necessary, however, before SMVs can be safely used in humans. The SMV aortic counterpulsator model is reproducible and has functioned beyond four years. In the past, however, the descending thoracic aorta was ligated between the two vascular grafts connecting the SMV to the aorta to obligate blood flow through the SMV. Clearly, ligating the aorta in a clinical situation is not ideal. During the current funding period, this model was modified so that the aorta was only narrowed by 50 percent. Complications developed in some of the animals, usually during the first two weeks. An adjustable occluding device to occlude the aorta is now proposed. We are certain this model can be made successful without complete aortic occlusion, but may require complete aortic occlusion (with blood flow to the distal aorta through the SMV) for the first two weeks after the SMV has been connected to the circulation and/or narrowing the aorta more than 50 percent. Appropriate experiments are proposed herein. The SMV left ventricular apex to aorta configuration is the most hemodynamically effective skeletal muscle cardiac assist device that we have tested. Prior to our last funding, this was an acute model, and attempts to go long term resulted in thrombosis of this model within two weeks. Recently, this model has functioned well for beyond six months. More refinement and testing is needed, however, before the LV apex-to- aorta-SMV can be used clinically. This proposal contains necessary studies to achieve that goal.